In Cairns, it’s best to leave the center a bit and park somewhere in a side street. We have been changing places every time during our one month stay. If you get caught, and we met people who did, just tell the ranger, that you have arrived in Cairns late at night and didn’t have anywhere to go. But in any case, if you drive out of the city enough, you should be more than fine.
Do not stay near the beach overnight. You can park there and go party, but don’t sleep in your car there.
We also often stayed near the beach, across from the skatepark, right by the Rydges Resort. I put this place on the map, it’s kinda neat place. You should stay there if your car or van is obviously a backpacking car – like a Jucy rental car for example. This place is somehow so obvious and at the same time hidden, we were fine for weeks.
During the day you can shower, chill, BBQ, flirt and I don’t know what else at the lagoon of Cairns.